1. Field of the Invention
This invention relates to the structure of a CRT (Cathode-Ray-Tube) socket for connecting a cathode ray tube used in a color television, etc., and particularly relates to a CRT socket for reliably insulating a focus contact and a signal contact from each other.
2. Description of the Background Art
Referring now to FIGS. 9 and 10, a base insertion hole 101, in a conventional CRT socket 100, is formed in an insulating housing 102. A plurality of signal contacts 103, 103, xe2x80x94and focus contacts 104, 104, xe2x80x94are formed at predetermined intervals in the insulating housing 102, around the outside of the base insertion hole 101, on the same circular circumference concentric to the base insertion hole 101.
A columnar base 100a of a CRT tube is inserted into the base insertion hole 101 and connected from a front face side (an upper side in FIG. 10) of the CRT socket 100 to the base insertion hole 101. A signal pin 100b and a focus pin 100c, arranged on the same circular circumference around the base 100a, respectively, are in physical and electrical contact with the signal contact 103 and the focus contact 104 facing the front face side.
The signal contact 103 and the focus contact 104 both have a conductive metallic plate that has been press-worked and formed in a bottle type (sometimes known as a banana plug) in which a connecting portion has a cylindrical shape and a drawn intermediate portion. The columnar signal pin 100b and the focus pin 100c are inserted into the drawn portion and are secured in place by a predetermined contact pressure.
A neck diameter of the cathode ray tube is reduced to make the cathode ray tube compact. As a result, the attaching positions of the contacts 103, 104 in the insulating housing 102 are closely spaced to each other. Accordingly, there is a concern that the focus contact 104 and the signal contact 103 are short-circuited along a surface of the insulating housing 102 since a high voltage of several thousands volts is applied to the focus pin 100c. To reduce the chance of such arc-over, the insulating housing 102 includes a ring-shaped portion 105 attached to the signal contact 103, a cover portion 106 attached to, the focus contact 104, and a base portion 109 covering the rear of the cover portion 106.
Creepage is defined as the conduction of electricity across the surface of a dielectric. A creepage distance is the distance along a dielectric that such conduction must occur for an arc to be formed. The creepage distance in the prior-art device is the distance along the surface of the insulating housing 102 between the focus contacts 104 and the signal contacts 103. The creepage distance is extended by interposing a slit 107 between the ring-shaped portion 105 and the cover portion 106. The rear face of a focus contact storing chamber 108 for storing a contact portion of the focus contact 104 is covered with the base portion 109. This construction reduces the chance of the above short circuit.
Referring now also to FIG. 11, the gap (L) between the base 100a and the focus pin 100c is very narrow to reduce the neck diameter of the cathode ray tube. In the conventional CRT socket 100, the focus contact 104 and a partition wall 106a of the cover portion 106 are interposed in this gap (L). Therefore, the thickness of the partition wall 106a is limited to a value that is less than desired. As a result, the strength of the partition wall 106a for partitioning the focus contact storing chamber 108 and the base insertion hole 101 is insufficient. Therefore, there is a chance that the partition wall 106a will be damaged when the cathode ray tube is forced into the socket at a slant when making the connection.
The rear face of the focus contact storing chamber 108 is covered by the base portion 109. A short-circuited electric current flows to an abutting portion of the cover portion 106 and the base portion 109, i.e., a rear face side of the ring-shaped portion 105 via a rear face of the partition wall 106. Accordingly, the distance between the focus contact 104 and the signal contact 103 cannot be made great enough to avoid arc-over.
To solve the above problems, an object of this invention is to provide a CRT socket in which a partition wall for partitioning a focus contact storing chamber and a base insertion hole has sufficient strength, and the creepage distance between a focus contact and a signal contact can be set to a sufficient length.
To solve the above problems, a CRT socket of the invention comprises an insulating housing in which the insulating housing is constructed by a ring-shaped portion in which a cylindrical base insertion hole is bored and plurality of signal contact storing chambers are concavely arranged from a rear face side on an outside circular circumference of the base insertion hole; a cover portion for arranging a focus contact storing chamber on the same circular circumference as the signal contact storing chambers by projecting a projecting portion concavely having the focus contact storing chamber from the rear face side to a portion having no ring-shaped portion; and a base portion for covering the rear face side of the cover portion; and the cover portion and the base portion are integrated with each other by molding the ring-shaped portion integrally with the cover portion or the base portion, and engaging the cover portion and the base portion with each other; a signal contact stored in each signal contact storing chamber; and a focus contact stored in the focus contact storing chamber; wherein a pin insertion hole communicated with the signal contact storing chamber and the focus contact storing chamber from front face sides of the ring-shaped portion and the projecting portion is bored, and a signal pin and a focus pin of a cathode ray tube arranged on an outside circular circumference of a base are respectively electrically connected to the signal contact and the focus contact, the CRT socket includes the focus contact constructed by a conductive metallic plate of a band shape, and an intermediate portion of the conductive metallic plate is bent at an acute angle, a bent basic end side is set to a supporting portion, and a bent tip side is set to a leaf spring contact portion; the supporting portion rises and is supported along an inner wall face of the focus contact storing chamber facing a direction of the base insertion hole, and the leaf spring contact portion faces the pin insertion hole; and an outside face of the projecting portion is covered with a partition wall rising on the front face side from the base portion.
The focus contact is formed in a leaf type in which an intermediate portion of the metallic plate of a band shape is bent at an acute angle. A supporting portion of the focus contact rises and is supported along an inner wall face facing the direction of the base insertion hole. Therefore, there is no focus contact interposed in a gap (L) between the base and the focus pin in the cathode ray tube. Accordingly, it is possible to increase the thickness of the partition wall to a thickness of the focus contact from the base portion, and cover the outside face of the projecting portion.
Since the partition wall of the base portion overlaps the, outside of a partition wall of the projecting portion, increased strength is obtained in the partition wall for partitioning the focus contact storing chamber and the base insertion hole.
The distance between the focus contact and the signal contact is extended by the partition wall rising from the base portion sufficiently to achieve sufficient length for mutual insulation.
The CRT socket of the invention includes the ring-shaped portion and the base portion being integrally molded. The cover portion is engaged with the base portion and is attached to the front face side of the base portion.
The signal contact is stored in the signal contact storing chamber concavely arranged from the rear face side of the ring-shaped portion. The focus contact is stored in the focus contact storing chamber concavely arranged in the cover portion.
Since the cover portion is engaged with the front face side of the base portion integrated with the ring-shaped portion, the focus contact is stored on the front face side and the signal contact is stored on the rear face side through the ring-shaped portion and the base portion. Accordingly, the distance between the focus contact and the signal contact can be easily lengthened.
The CRT socket according to a further embodiment of the invention includes a base portion formed in a box shape in which the partition wall rises along a peripheral portion of the base portion, and the cover portion is formed in a contour shape internally fitted to the box shape.
Since the base portion is formed in a box shape, the base portion is easily positioned with respect to the cover portion, and the base portion and the cover portion engage each other without rattling.
The CRT socket of the invention is characterized in that a pair of projecting portions forked into two branches is formed in the cover portion, and the focus contact is stored in the focus contact storing chamber of each projecting portion.
The outside face of the projecting portion is also covered with the partition wall rising from the base portion even in a double focus type having a pair of focus contacts. Accordingly, the distance between the respective focus contacts, or the distance between each focus contact and the signal contact can be set to a sufficient length to provide insulation.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.